Endothermic and exothermic chemical reactions can become violent if reactants are combined in an uncontrolled manner or if the ratio in which the reactants are combined is not correct. Even in the absence of a violent reaction, an incorrect combination of reactants can lead to the formation of unwanted byproducts and a poor yield of a desired product. Safe operation of equipment to run such reactions relies upon an operator to set flow rates in a proper ratio. Unfortunately, the same precision pumps and flow controls that ensure a proper molar ratio of reactants will likewise ensure that the wrong ratio is maintained if incorrect initial settings are used. Such systems have no built-in safeguard to prevent an operator from inadvertently setting up the equipment to make an unsafe combination of reactants. This problem is particularly exemplified by the reaction of bleach and ammonia to produce monochloramine.
The minimum amount of monochloramine that can be produced by commercial generation equipment available today is over one hundred pounds of NH2Cl per day. While this quantity is appropriate for large-scale industrial applications (paper mills, electric utility generating plants, and the like), there are many smaller-scale applications (reverse-osmosis systems, cooling towers for office buildings, and the like) that require only one-tenth (or less) of the minimum amount that existing commercial units produce. Reducing the size of the equipment is not straightforward, because the safety features of the existing equipment rely upon the use of pumps and flow meters that can reliably deliver precise flow rates. Pumps and flow meters are available that will work with a similar level of precision at these low mL/minute flow rates; however, these devices would be expensive and would tend to be too delicate for typical industrial applications.
Existing techniques for evaluating a bleach:ammonia reaction product involve some sort of chemical analysis of the mixture, usually using on-line or off-line colorimetric measurements. There are drawbacks to the use of these colorimetric techniques. Such measurement techniques take several minutes to complete; and during this time interval, a violent, out-of-control reaction can occur. The use of one or more reagents, which must be replenished periodically, is required. In the on-line measurement equipment, the reagents are fed using peristaltic pumps, which must be serviced periodically. The colorimetric techniques are very sensitive and must be used with very dilute samples at low ppm levels, requiring that a concentrated sample, containing 1% monochloramine or more, would typically have to be diluted by a factor of 100-1000.